1. Field of the Invention
This invention relates to extrusion process apparatus and more particular to an improved device to sever or to cut an outsided extrudate feeding into a liquid filled cooling chamber for cooling the molten extrudate.
2. Description of the Prior Art
It is known to form certain types of continuous stock workpieces, such as rod and tubular shaped articles, from thermoplastic material by extruding the same as a heated extrudate from an extruder followed by passage of the heated extrudate through a cooling bath to remove heat therefrom so as to set or rigidize the material of the continuous stock which thereafter may be sectioned into individual articles for a particular intended end use. The extrudate further may be shaped and sized by passing the same through a closing or sizing aperture located advantageously at the entrance to the cooling bath. U.S. Pat. Nos. 3,538,210 and 3,579,623 both describe methods with which tubular articles can be made, such articles being characterized by having circumferential dimension of precise nature within a particular range of values. As is well-known in the extrusion art, and as is exemplified by the aforementioned patents, the extrudate if it is in tubular form generally will be issued from the extruder at a size somewhat larger than the final finished product and then directed through the sizing aperture to draw down the extrudate to the requisite final dimension. The extrudate will have, for formation of a workpiece of given size and with respect to the extrudate line speed and placement of extruder in relation to the cooling bath entrance, a predetermined dimension during its travel from the extruder to the sizing aperture, such predetermined dimension diminishing uniformally as the extrudate approaches the closing aperture.
If for any reason the extrudate should leave the extruding means at an outsized dimension, that is at a dimension greater than intended either by way of overall workpiece diameter at any given location, or by reason of foreign material in the extrudate, degradation of the extrudate or other factors which might cause the extrudate to have a greater thickness of the tube wall then intended, it is possible for the outsized extrudate upon entry through the closing aperture to jam the same. This can result in shutdown of the forming line apparatus as well as requiring that the aperture be freed, a not easy task because the plastic state extrudate when solidified in the aperture is difficult and time consuming to remove. Furthermore, if the extrudate were outsized to a point that it would cause a jam in the sizing aperture and a breakage in the extrudate occurred without fully jamming the sizing aperture, it is probable that cooling liquid from the bath thereof would escape through the aperture and splash onto adjacent machinery including the extruding apparatus to the detriment of the latter.
In a related U.S. Pat. No. 3,813,200, assigned to the assignee of this invention, there is disclosed a jam prevention device operative with an extrusion process apparatus, of which the present invention is an improvement. More specifically, there is disclosed in U.S. Pat. No. 3,813,200 a device responsive to the detection of an outsided extrudate for severing the extrudate feeding through an entrance sizing aperture and into a liquid filled cooling chamber and including a cutter blade mounted to move in a rectalinear motion from a first position to a second position, whereby a cutting edge of the cutter blade moves past the entrance sizing aperture to thereby cut or sever the extrudate at that aperture. Further, a photoelectric cell detection unit is provided in close proximity to the entrance sizing aperture. If the extrudate is outsized with respect to a desired predetermined dimension, the outsided extrudate interrupts the light beam to cause the cutter blade to move from its first to its second position. In the noted patent, the cutter blade has but a single cutting edge that acts in a manner of a "guillotine" to sever the extrudate. It has been found out in the use of such a device that the guillotine type of cutting action is relatively slow so that an undesired amount of outsized extrudate may build up before the cutter blade is able to sever it. Further, the single cutting edge tends to become dull necessating the shutdown of the extrusion process apparatus to permit a new cutter blade to be inserted therein. Such frequent shutdowns are of course undesirable in that continued manufacture is interrupted.